- Radiocarbon (14C) dating is often used to obtain an absolute date for recent organic materials.
- Carbon-12 (12C) is a stable carbon isotope.
- Cosmic rays convert 14N to carbon-14. 14C is radioactive.
- The carbon in atmospheric carbon dioxide (CO2) is mostly 12C, but a very small amount is 14C.
- Living plants take up CO2. Plants are eaten by animals. Living organisms have a small amount of 14C in them.
- Although the 14C continually disappears (decays) in the organism, it is balanced by the uptake of more 14C.
- When the organism dies, the uptake of 14C ceases.
- The radioactive decay continues until all the 14C is converted back to N-14.
- We can estimate the age of the organism's death by the 14C / 12C ratio.
Use the graph to help answer these questions:
- What is the definition of half-life?
- How many years does it take for 50% of the 14C to decay? ______
- How many years until only 10% of the 14C is left?_______
- If you have a plant specimen with 25% of its 14C left, how many half-lives have passed? ______
- How old in years is that plant specimen in the question above? ______
- If a bone artifact is 35,000 years old, what percentage of the 14C would be left? ______
- Explain why is the practical limit for dating with 14C about 40,000 years.